This invention relates to the live insertion of circuit boards into a chassis or card cage, commonly referred to as xe2x80x9chot-swappingxe2x80x9d the circuit boards. This allows a faulty board to be swapped out of a communication or electronic system and replaced by an operative board while the system remains up and running.
There are various known communication systems which incorporate circuit boards capable of live insertion into a hot chassis back plane or motherboard. In such systems, a switch is mounted to each circuit board, the switch controlling the power to the circuit board. In other words, the switch is connected between the power bus on the motherboard and the motherboard connector which couples power to the circuit board plugged into that connector. Often the switch is mounted near the front edge of the board and is closed after the circuit board is inserted into its appropriate slot in the chassis by the movement of that board""s injector latch to its locking position or by the closure of a cover over that latch. In other cases, the power switch is located on the circuit board so as to be closed upon contact by the back plane or motherboard connector receiving that circuit board. Examples of the foregoing hot plug switch mechanisms are disclosed in U.S. Pat. No. 5,530,302.
Prior switch mechanisms of this type are disadvantaged in that they take up space on the printed circuit board where space is at a premium. Also, the prior switch mechanisms often comprise mechanical push button switches which do not always open and close when they should due to mechanical tolerances built into the chassis supporting the circuit boards. In other words, the closing of a printed circuit board""s injector latch or latch cover may not always or reliably close the power switch on that circuit board. Furthermore, they are relatively expensive and are sometimes adversely affected by mechanical shock and vibration.
Accordingly it is an object of the present invention to provide an improved hot plug switch mechanism for controlling power to a printed circuit board when hotswapping that board.
An additional object is to provide a switch mechanism of this type which allows greater freedom in the layout of the board whose power is being controlled.
Another object of the invention is to provide such a switch mechanism which does not take up any space on the circuit board whose power is being controlled by that switch.
Still another object of the invention is to provide a hot plug switch mechanism which is relatively inexpensive.
A further object of the invention is to provide a hot plug switch mechanism which is reliable and relatively immune to vibration and other environmental effects.
The invention accordingly comprises the features of constructions, combination of elements and arrangement of parts which will be exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.
Briefly, my hot plug switch mechanism controls the power to a printed circuit board inserted into the slot of a card cage or chassis in order to interface with a motherboard in the chassis. Instead of installing the power switch on the printed circuit board as has been done heretofore, it is mounted to the motherboard and opened and closed by an actuator assembly mounted to the chassis adjacent to the card slot for containing the printed circuit board to be controlled by that switch. In accordance with the invention, the power switch is an electronic proximity switch, preferably a Hall Effect switch, and the plunger mechanism includes a housing mounted to the chassis opposite the switch and a plunger slidably received in that housing. One end of the plunger facing the switch carries a magnet; the opposite end of the plunger is located adjacent to the entrance to the card slot for containing the associated circuit board. The plunger is movable in its housing toward and away from the motherboard and the switch thereon between an extended position which places the magnet sufficiently near the switch that the magnet""s field closes the switch so that electrical power is delivered to the corresponding printed circuit board in the card slot, and a retracted position wherein the magnet is spaced far enough away from the switch that the switch opens and interrupts power to the circuit board. The plunger is normally biased to its retracted position, but may be moved to its extended position by the closure of a cover located at the entrance to the slot for the corresponding printed circuit board.
The usual card chassis contains positions or slots for many circuit boards. In accordance with this invention, the chassis includes a separate hot plug switch mechanism for each circuit board position.
When a printed circuit board is properly seated in its slot in the card chassis, the cover at the entrance to that slot being closed, the plunger of the corresponding actuator assembly is maintained in it""s extended position so that the magnet at the end of that plunger is in close proximity to the corresponding power switch on the motherboard. As a result, the switch remains closed so that power is delivered to the corresponding circuit board. If for some reason it becomes necessary to remove that board from the card chassis, the cover at the entrance to the card slot containing that circuit board first has to be opened. As soon as the cover is opened, the plunger of the actuator assembly controlling the printed circuit board in that slot is released and springs to its retracted position. Since the magnet at the end of that plunger is no longer proximate the corresponding switch on the motherboard, that switch opens thereby disconnecting the circuit board in that slot from the power bus on the motherboard. The circuit board can then be removed from its slot in the chassis without effecting other circuit boards in the chassis or the operation of the system as a whole.
When a replacement board is inserted into the card slot, it is not powered up until the cover at the entrance to that slot is closed in order to secure that board in place. The closure of the cover moves the plunger of the corresponding actuator assembly to its extended position which places the magnet at the end of the plunger proximate to the Hall Effect switch on the motherboard. Resultantly, the magnet""s field closes that switch thereby connecting the printed circuit board to the power source only after the circuit board has interfaced or connected with the motherboard.
It should be understood that the circuit board and/or motherboard may be provided with conventional control logic circuitry for detecting power loss when the hot plug switch mechanism is opened and for gradually removing power just prior to the disconnecting of the circuit board from the motherboard and for ramping up board power after insertion of a fresh circuit board and the closing of the corresponding power switch; see e.g. U.S. Pat. No. 5,530,302.
Thus, any circuit board in the card chassis can be removed and replaced without appreciably affecting the operation of the other circuit boards in the chassis. Since the hot plug switch mechanism which controls the power to each circuit board comprises a simple inexpensive electronic switch on the motherboard which is actuated by a plunger mechanism on the chassis, more real estate is available on the circuit boards for logic and other purposes. Also, the utilization for the power switch of an electronic proximity switch such as a Hall Effect switch in lieu of the typical mechanical switches provides additional advantages in terms of lower cost and greater reliability.